Phosphor and light emitting device

ABSTRACT

A phosphor and a light emitting device including the phosphor may be provided that emits light having a peak wavelength between a green wavelength band and a yellow wavelength band, has a crystal structure of which the chemical formula is MSi 2 N 2 O 2 , M=Ca x Sr y Eu z  (x+y+z=1), and has a triclinic system crystal structure in which, when molar ratios of Ca, Sr and Eu are x, y and z respectively, x+y+z=1 and when the x, y and z are represented by a triangular projection, the x, y and z are distributed on the lines and at the inside of an area formed by connecting five points of (0.45, 0.55, 0), (0.75, 0.25, 0), (0.75, 0, 0.25), (0.5, 0, 0.5) and (0.45, 0.05, 0.5) by a solid line on a triangular diagram.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119(e) ofKorean Patent Application No. 10-2012-0077940 filed on Jul. 17, 2012,which is hereby incorporated by reference in its entirety.

BACKGROUND

1. Field

The present invention relates to a phosphor and a light emitting device.

2. Description of Related Art

A phosphor is excited by light with a particular wavelength and emitslight with a wavelength different from the particular wavelength. Such aphosphor is widely used together with a light emitting diode (LED).

Conventional phosphors have some problems. First, the conventionalphosphors have weak emission intensity in a visible light region(including a blue wavelength). Secondly, a wavelength of the emittedlight does not match an ideal peak wavelength. Thirdly, the emissionintensity is reduced with temperature increase. For example, as atemperature rises, luminance of the phosphor is reduced (ThermalQuenching).

Meanwhile, a variety of conventional phosphors include an oxide basedfluorescent material using rare earth elements. The oxide basedfluorescent materials has been already widely known and some of theoxide based fluorescent materials are now being actually used. However,unlike the oxide based fluorescent material used in CCFL for PDP, CRTand LCD, an oxide based fluorescent material for LED is required toefficiently emit light by ultraviolet rays and light having a bluewavelength.

The above references are incorporated by reference herein whereappropriate for appropriate teachings of additional or alternativedetails, features and/or technical background.

SUMMARY

One embodiment is a phosphor which emits light having a peak wavelengthbetween a green wavelength band and a yellow wavelength band, has acrystal structure of which the chemical formula is MSi₂N₂O₂,M=Ca_(x)Sr_(y)Eu_(z) (x+y+z=1), and has a triclinic system crystalstructure in which, when molar ratios of Ca, Sr and Eu are x, y and zrespectively, x+y+z=1 and when the x, y and z are represented by atriangular projection, the x, y and z are distributed on the lines andat the inside of an area formed by connecting five points of (0.45,0.55, 0), (0.75, 0.25, 0), (0.75, 0, 0.25), (0.5, 0, 0.5) and (0.45,0.05, 0.5) by a solid line on a triangular diagram.

Another embodiment is a phosphor which emits light having a peakwavelength between a green wavelength band and a yellow wavelength band,has a crystal structure of which the chemical formula is MSi₂N₂O₂,M=Ca_(x)Sr_(y)Eu_(z) (x+y+z=1), and has a triclinic system crystalstructure in which, when molar ratios of Ca, Sr and Eu are x, y and zrespectively, x+y+z=1 and when the x, y and z are represented by atriangular projection, the x, y and z are distributed on the lines andat the inside of an area formed by connecting five points of (0.45, 0.4,0.15), (0.75, 0.1, 0.15), (0.75, 0, 0.25), (0.6, 0, 0.4) and (0.45,0.15, 0.4) by a solid line on a triangular diagram. A unit cell volumeof the triclinic system crystal structure is greater than 700 Å³.

Further another embodiment is a light emitting device including: a lightemitting element; and a phosphor which is excited by a part of lightemitted from the light emitting element and emits light having awavelength different from that of the light emitted from the lightemitting element. The phosphor emits light having a peak wavelengthbetween a green wavelength band and a yellow wavelength band, has acrystal structure of which the chemical formula is MSi₂N₂O₂,M=Ca_(x)Sr_(y)Eu_(z) (x+y+z=1), and has a triclinic system crystalstructure in which, when molar ratios of Ca, Sr and Eu are x, y and zrespectively, x+y+z=1 and when the x, y and z are represented by atriangular projection, the x, y and z are distributed on the lines andat the inside of an area formed by connecting five points of (0.45,0.55, 0), (0.75, 0.25, 0), (0.75, 0, 0.25), (0.5, 0, 0.5) and (0.45,0.05, 0.5) by a solid line on a triangular diagram.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 is a cross sectional view of a light emitting device according toan embodiment;

FIG. 2 is a cross sectional view of a light emitting device according toanother embodiment;

FIG. 3 is a view representing x, y and z on coordinate axes of atriangular diagram;

FIG. 4 is a triangular diagram representing by a solid line that lighthaving a peak wavelength close to a yellow wavelength band is emitted;

FIG. 5 is a triangular diagram representing x, y and z obtained byplotting the result shown in Table 1 on the coordinate axes of thetriangular diagram;

FIG. 6 is a triangular diagram representing an area by a solid line,which includes a case of a triclinic system beta (β) shown in FIG. 5;

FIG. 7 is a triangular diagram representing a predetermined sample Aincluded in a triclinic system beta (β) and a predetermined sample Bincluded in a triclinic system alpha (α) in the triangular diagramhaving x, y and z coordinate axes;

FIG. 8 is a graph showing a result of XRD analysis with respect to thesample A of FIG. 7;

FIG. 9 is a graph showing a result of XRD analysis with respect to thesample B of FIG. 7;

FIG. 10 is a triangular diagram obtained by plotting a case where lighthaving a peak wavelength close to a yellow wavelength band is emitted;

FIG. 11 is a triangular diagram representing by a solid line that lighthaving a peak wavelength close to a yellow wavelength band is emitted;

FIG. 12 shows excitation spectrums of phosphors respectively inaccordance with a first to a fourth embodiments;

FIG. 13 shows light emission spectrums of phosphors respectively inaccordance with the first to the fourth embodiments;

FIG. 14 is a graph showing quantum efficiencies based on strontiumratios of the first to the fourth embodiment and a first to a fifthcomparison examples;

FIG. 15 is a graph showing X-ray diffraction patterns of the first tothe fourth embodiment and the first to the fifth comparison examples;and

FIG. 16 shows results obtained by plotting the first to the fourthembodiment and the first to the fifth comparison examples on atriangular diagram representing x, y and z on coordinate axes thereof.

DETAILED DESCRIPTION

A thickness or a size of each layer may be magnified, omitted orschematically shown for the purpose of convenience and clearness ofdescription. The size of each component may not necessarily mean itsactual size.

It should be understood that when an element is referred to as being‘on’ or “under” another element, it may be directly on/under theelement, and/or one or more intervening elements may also be present.When an element is referred to as being ‘on’ or ‘under’, ‘under theelement’ as well as ‘on the element’ may be included based on theelement.

An embodiment may be described in detail with reference to theaccompanying drawings.

<Phosphor>

Hereafter, a phosphor according to an embodiment of the presentinvention will be described in detail.

The phosphor according to an embodiment of the present invention isexcited by ultraviolet ray and light having a peak wavelength in a bluewavelength band close to the ultraviolet ray, and then emits lighthaving a peak wavelength between a green wavelength band and a yellowwavelength band. The phosphor according to the embodiment of the presentinvention is excited by light having a peak wavelength in a wavelengthband of 400 nm to 480 nm, and then emits light having a peak wavelengthin a wavelength band of 500 nm to 600 nm.

The phosphor according to the embodiment of the present invention has atriclinic system crystal structure containing three components of Ca, Srand Eu.

When molar ratios of Ca, Sr and Eu included in the phosphor according tothe embodiment of the present invention are x, y and z respectively,x+y+z=1. When the x, y and z are represented by a triangular projection,the x, y and z are distributed on the lines and at the inside of an areaformed by connecting five points of (0.45, 0.55, 0), (0.75, 0.25, 0),(0.75, 0, 0.25), (0.5, 0, 0.5), (0.45, 0.05, 0.5) by a solid line on atriangular diagram.

FIG. 3 is a view representing the x, y and z on coordinate axes of atriangular diagram. The x, y and z, i.e., molar ratios of Ca, Sr and Euincluded in the phosphor according to the embodiment of the presentinvention are included on the lines and at the inside of the solid-linearea in the triangular diagram of FIG. 3.

The phosphor according to the embodiment of the present invention may bean oxy-nitride based phosphor.

The chemical formula of the phosphor according to the embodiment may beMSi₂N₂O₂, M=Ca_(x)Sr_(y)Eu_(z) (x+y+z=1). Here, when the molar ratios ofCa, Sr and Eu are x, y and z respectively, x+y+z=1. When the x, y and zare represented by the triangular projection, the x, y and z aredistributed on the lines and at the inside of the area formed byconnecting five points of (0.45, 0.55, 0), (0.75, 0.25, 0), (0.75, 0,0.25), (0.5, 0, 0.5), (0.45, 0.05, 0.5) by a solid line on thetriangular diagram. In particular, the oxy-nitride based phosphoraccording to the embodiment of the present invention has an excellentlight emitting property under such composition. That is, the intensityand luminance of light emitted from the phosphor according to theembodiment are improved. Also, the phosphor is less affected by anambient temperature.

The phosphor according to the embodiment of the present invention mayhave a crystal structure of triclinic system.

Within the same range, particularly, when the molar ratio z of Eu isfrom 0.15 to 0.4, the oxy-nitride based phosphor according to theembodiment of the present invention emits light having a peak wavelengthparticularly close to the yellow wavelength band among the greenwavelength band and the yellow wavelength band. In other words, when themolar ratio z of Eu is from 0.15 to 0.4, the aforementioned phosphoraccording to the embodiment of the present invention emits light havinga peak wavelength particularly close to 560 nm among in the wavelengthband of 500 nm to 600 nm. FIG. 4 is a view representing the x, y and zon the coordinate axes of the triangular diagram. FIG. 4 represents by asolid line the range of light having a peak wavelength close to a yellowwavelength band is emitted. In FIG. 4, the x, y and z, i.e., the molarratios of Ca, Sr and Eu included in the phosphor according to theembodiment of the present invention are included on the lines and at theinside of the solid-line area.

When the oxy-nitride based phosphor has particularly a predeterminedcrystal structure that the inventor of the present invention hasdiscovered among the crystal structures of triclinic system, it has amore excellent light emitting property. In this specification, a crystalstructure having particularly excellent light emitting property amongthe crystal structures of triclinic system is referred to as triclinicsystem beta (β), and a crystal structure having no excellent lightemitting property is referred to as triclinic system alpha (α). However,so long as a crystal structure having the function and effect of thepresent invention is included in the concept overall described in thisspecification, the crystal structure is not necessarily limited to aspecific name.

The intensity and luminance of the light emitted from the phosphoraccording to the embodiment of the present invention, i.e., the phosphorhaving the beta (β) crystal structure of the triclinic system isimproved as compared with those of the light emitted from the phosphorhaving no beta (β) crystal structure of the triclinic system. Inaddition, the phosphor having the beta (β) crystal structure of thetriclinic system is less affected by an ambient temperature as comparedwith the phosphor having no beta (β) crystal structure of the triclinicsystem.

Quantum efficiency, particularly, internal quantum efficiency may beemployed as one of methods for estimating the light emission efficiencyof the phosphor according to the embodiment. The embodiment-basedphosphor having a predetermined crystal structure, i.e., the beta (β)crystal structure of the triclinic system has more excellent internalquantum efficiency than that of the phosphor having no beta (β) crystalstructure of the triclinic system.

Table 1 shows that a case where the phosphor has the triclinic systembeta (β) crystal structure is represented by “∘” and a case where thephosphor has the triclinic system alpha (α) crystal structure isrepresented by “x”, through the experimental results of x, y and z, thatis, the molar ratios of Ca, Sr and Eu by means of various values. FIG. 5is a triangular diagram representing x, y and z obtained by plotting theresult shown in Table 1 on the coordinate axes of the triangulardiagram.

TABLE 1 No. x Y z β phase 1 0.4 0 0.6 x 2 0.45 0 0.55 x 3 0.5 0 0.5 ∘ 40.55 0 0.45 ∘ 5 0.6 0 0.4 ∘ 6 0.7 0 0.3 ∘ 7 0.75 0 0.25 x 8 0.8 0 0.2 x9 0 1 0 x 10 1 0 0 x 11 0.95 0 0.05 x 12 0.7125 0.2375 0.05 ∘ 13 0.633330.31667 0.05 ∘ 14 0.55417 0.39583 0.05 ∘ 15 0.475 0.475 0.05 ∘ 160.39583 0.55417 0.05 x 17 0.31667 0.63333 0.05 x 18 0.2375 0.7125 0.05 x19 0.6365 0.3135 0.05 ∘ 20 0.61975 0.30525 0.075 ∘ 21 0.603 0.297 0.1 ∘22 0.58625 0.28875 0.125 ∘ 23 0.5695 0.2805 0.15 ∘ 24 0.55275 0.272250.175 ∘ 25 0.536 0.264 0.2 ∘ 26 0.48 0.32 0.2 ∘ 27 0.58575 0.23925 0.175∘ 28 0.568 0.232 0.2 ∘ 29 0.495 0.33 0.175 ∘ 30 0.55275 0.27225 0.175 ∘31 0.58575 0.23925 0.175 ∘ 32 0 0 1 x 33 0.5 0.2 0.3 ∘ 34 0.5 0.4 0.1 ∘35 0.6 0.1 0.3 ∘ 36 0.7 0.1 0.2 ∘ 37 0.5 0.1 0.4 ∘ 38 0.6 0.3 0.1 ∘ 390.45 0.55 0 ∘ 40 0.7 0.3 0 ∘ 41 0.4 0.3 0.3 x 42 0.4 0.2 0.4 x 43 0.40.5 0.1 x 44 0.4 0.6 0 x 45 0.5 0.5 0 ∘ 46 0.65 0.35 0 ∘ 47 0.75 0.25 0x 48 0.8 0.2 0 x 49 0.85 0.15 0 x

FIG. 6 is a triangular diagram representing an area by a solid line,which includes a case of a triclinic system beta (β) shown in FIG. 5. Asshown in FIG. 6, when x, i.e., the molar ratio of Ca, y, i.e., the molarratio of Sr and z, i.e., the molar ratio of Eu are represented oncoordinate axes of the triangular diagram, the coordinate values of x, yand z are located on the lines and at the inside of an area formed byconnecting four points of A (0.45, 0.55, 0), B (0.75, 0.25, 0), C (0.7,0, 0.3) and D (0.5, 0, 0.5) as vertices. As can be seen referring toTable 1 and FIG. 6, when the phosphor is located in such a range, it hasparticularly an excellent light emitting property. For example, thephosphor included in such a range has excellent internal quantumefficiency.

The phosphor located in the range shown in FIG. 6 has a predeterminedcrystal structure, i.e., the beta (β) crystal structure of the triclinicsystem while the phosphor located outside the range does not have.

An X-ray diffraction (XRD) analysis method may be used to identify thecrystal structure. Through the XRD analysis, the analysis result of thecrystal structure that the embodiment-based phosphor has, that is, thetriclinic system beta (β) crystal structure is different from that ofnon-triclinic system beta (β) crystal structure, i.e., the triclinicsystem alpha (α) crystal structure.

FIG. 7 is a triangular diagram representing a predetermined sample Aincluded in a triclinic system beta (β) and a predetermined sample Bincluded in a triclinic system alpha (α) in the triangular diagramhaving x, y and z coordinate axes.

FIG. 8 is a graph showing a result of XRD analysis with respect to thesample A of FIG. 7. FIG. 9 is a graph showing a result of XRD analysiswith respect to the sample B of FIG. 7. As can be seen referring to theXRD analysis result of FIGS. 8 and 9, the beta (β) crystal structure ofthe triclinic system according to the embodiment has an analysis resultdifferent from that of non-beta (β) crystal structure of the triclinicsystem.

Within the same range in which the oxy-nitride based phosphor has thebeta (β) crystal structure of the triclinic system, particularly when z,i.e., the molar ratio of Eu is from 0.15 to 0.4, the oxy-nitride basedphosphor according to the embodiment emits light having a peakwavelength particularly close to the yellow wavelength band among thegreen wavelength band and the yellow wavelength band. That is, when themolar ratio z of Eu is from 0.15 to 0.4, the oxy-nitride based phosphoremits light having a peak wavelength particularly close to 560 nm amongin the wavelength band of 500 nm to 600 nm.

Table 2 shows coordinate values of x, y and z when the phosphor has thetriclinic system beta (β) crystal structure and a peak wavelength closeto the yellow wavelength band through the experimental results of x, yand z, that is, the molar ratios of Ca, Sr and Eu by means of variousvalues. FIG. 10 is a triangular diagram obtained by plotting a casewhere light having a peak wavelength close to a yellow wavelength bandis emitted. In FIG. 10, circular plots mean that the light having a peakwavelength close to the yellow wavelength band is emitted. FIG. 11 is aview representing the x, y and z on the coordinate axes of thetriangular diagram. FIG. 11 represents by a solid line the range oflight having a peak wavelength close to a yellow wavelength band isemitted. In FIG. 11, the x, y and z, i.e., the molar ratios of Ca, Srand Eu included in the embodiment-based phosphor emitting the lighthaving a peak wavelength close to the yellow wavelength band areincluded on the lines and at the inside of the solid-line area.

TABLE 2 No. X y z 1 0.58575 0.23925 0.175 2 0.568 0.232 0.2 3 0.56950.2805 0.15 4 0.55275 0.27225 0.175 5 0.536 0.264 0.2 6 0.527 0.323 0.157 0.48 0.32 0.2 8 0.7 0 0.3 9 0.6 0 0.4 10 0.7 0.1 0.2 11 0.6 0.1 0.3 120.5 0.2 0.3 13 0.5 0.1 0.4

Hereafter, a method for manufacturing the phosphor according to theembodiment will be described. The below-described method is only anexample. It is not necessarily to depend on the following specificmethod to be described below. In order to manufacture the phosphorhaving a predetermined composition according to the embodiment and thephosphor having the crystal structure, it is possible to change aportion of the following manufacturing method.

Carbonate of alkali earths metal M, SiO₂, Si₃N₄ and Eu₂O₃ are mixed in apredetermined ratio until they are uniformly mixed, and thus a compositeis prepared. The carbonate of the alkali earths metal M may include, forexample, SrCO₃. Ca, Sr, Si, Eu metal, oxide, nitride, various salts andthe like may be used as the material of the carbonate. All or a portionof the material may be mixed with liquid, for example, as a solutionthereof. Also, SrF₂, BaF, H₃BO₄, NaCl and the like functioning as fluxmay be mixed together.

The composite is put into a boron nitride crucible, etc., and is firedin a reduction atmosphere or in an inert atmosphere, and thus a firedmaterial is formed. An alumina crucible as well as the boron nitridecrucible may be used. A firing temperature is from 1,400° C. to 1,700°C., and more preferably, from 1,450° C. to 1,600° C. Here, if the firingtemperature is lower than 1,400° C., the various materials may not reactwith each other or the phosphor having the triclinic system crystalstructure is not obtained. If the firing temperature is 1,700° C., thevarious materials are decomposed or molten themselves. When the firingtemperature is from 1,450° C. to 1,600° C., a probability that thevarious materials do not react with each other or are decomposed can bereduced.

The reduction atmosphere may be one of a H₂—N₂ atmosphere, an ammoniaatmosphere and a nitrogen-ammonia atmosphere. The inert atmosphere maybe one of a nitrogen atmosphere and an argon atmosphere. In the inertatmosphere, Eu³⁺ may be reduced into Eu²⁺.

Regarding the firing process, some of the materials are mixed and firedfirst. Then, the other materials are mixed with the fired materialobtained through the firing process and are fired. Consequently, anobjective phosphor may be obtained.

The fired material obtained through the firing process may be pulverizedand, for example, may be cleaned by water without impurities, e.g.,distilled water which has pH less than 8, refined water and the like.

The following whole process will be taken as a concrete example of themanufacturing process. That is, first, Sr₂SiO₄:Eu is obtained by causingSrCO₃, SiO₂ and Eu₂O₃ to react with each other, and then the Sr₂SiO₄:Euis pulverized. Subsequently, SrSi₂O₂N₂:Eu is obtained by causing thepulverized Sr₂SiO₄:Eu and Si₃N₄ to react with each other, and thenSrSi₂O₂N₂:Eu is pulverized. Then, the pulverized SrSi₂O₂N₂:Eu is cleanedby distilled water or refined water which has pH less than 8 andimpurities which have been removed as much as possible.

The following first to fourth embodiments show method for manufacturingthe phosphor according to the embodiment by changing the molar ratio ofstrontium (Sr). Here, the ratio of strontium (Sr) means that, when thesum of x, y and z, that is, the ratios of Ca, Sr and Eu within themanufactured phosphor is 1, a proportion that the strontium (Sr)occupies in 1.

First Embodiment

A composite obtained by mixing 16.35 g of SrCO₃, 12.04 g of SiO₂, 34.25g of Si₃N₄, 4.10 g of Eu₂O₃ and 33.26 g of CaCO₃ is put into a boronnitride crucible and then is fired in the reduction atmosphere usingH₂—N₂ mixture gas at a temperature of about 1,500° C. for about 6 hours.The ratio of strontium included in the product, i.e., phosphor is0.2375.

Second Embodiment

A composite obtained by mixing 21.43 g of SrCO₃, 11.83 g of SiO₂, 33.65g of Si₃N₄, 4.03 g of Eu₂O₃ and 29.05 g of CaCO₃ is put into a boronnitride crucible and then is fired in the reduction atmosphere usingH₂—N₂ mixture gas at a temperature of about 1,500° C. for about 6 hours.The ratio of strontium included in the product, i.e., phosphor is0.3135.

Third Embodiment

A composite obtained by mixing 26.33 g of SrCO₃, 11.63 g of SiO₂, 33.08g of Si₃N₄, 3.96 g of Eu₂O₃ and 24.99 g of CaCO₃ is put into a boronnitride crucible and then is fired in the reduction atmosphere usingH₂—N₂ mixture gas at a temperature of about 1,500° C. for about 6 hours.The ratio of strontium included in the product, i.e., phosphor is 0.399.

Fourth Embodiment

A composite obtained by mixing 31.07 g of SrCO₃, 11.44 g of SiO₂, 32.53g of Si₃N₄, 3.90 g of Eu₂O₃ and 21.06 g of CaCO₃ is put into a boronnitride crucible and then is fired in the reduction atmosphere usingH₂—N₂ mixture gas at a temperature of about 1,500° C. for about 6 hours.The ratio of strontium included in the product, i.e., phosphor is 0.475.

The following first to fifth comparison examples are intended to becompared with the first to the fourth embodiment.

First Comparison Example

A composite obtained by mixing 10.44 g of SiO₂, 33.72 g of Si₃N₄, 3.94 gof Eu₂O₃ and 42.55 g of CaCO₃ is put into a boron nitride crucible andthen is fired in the reduction atmosphere using H₂—N₂ mixture gas at atemperature of about 1,500° C. for about 6 hours. The ratio of strontiumincluded in the product, i.e., phosphor is 0.

Second Comparison Example

A composite obtained by mixing 35.65 g of SrCO₃, 11.25 g of SiO₂, 32.00g of Si₃N₄, 3.83 g of Eu₂O₃ and 17.26 g of CaCO₃ is put into a boronnitride crucible and then is fired in the reduction atmosphere usingH₂—N₂ mixture gas at a temperature of about 1,500° C. for about 6 hours.The ratio of strontium included in the product, i.e., phosphor is 0.551.

Third Comparison Example

A composite obtained by mixing 40.09 g of SrCO₃, 11.07 g of SiO₂, 31.48g of Si₃N₄, 3.77 g of Eu₂O₃ and 13.59 g of CaCO₃ is put into a boronnitride crucible and then is fired in the reduction atmosphere usingH₂—N₂ mixture gas at a temperature of about 1,500° C. for about 6 hours.The ratio of strontium included in the product, i.e., phosphor is 0.627.

Fourth Comparison Example

A composite obtained by mixing 44.38 g of SrCO₃, 10.89 g of SiO₂, 30.98g of Si₃N₄, 3.71 g of Eu₂O₃ and 10.03 g of CaCO₃ is put into a boronnitride crucible and then is fired in the reduction atmosphere usingH₂—N₂ mixture gas at a temperature of about 1,500° C. for about 6 hours.The ratio of strontium included in the product, i.e., phosphor is0.7125.

Fifth Comparison Example

A composite obtained by mixing 62.75 g of SrCO₃, 10.44 g of SiO₂, 33.72g of Si₃N₄, and 3.94 g of Eu₂O₃ is put into a boron nitride crucible andthen is fired in the reduction atmosphere using H₂—N₂ mixture gas at atemperature of about 1,500° C. for about 6 hours. The ratio of strontiumincluded in the product, i.e., phosphor is 0.95.

Through the first to the fourth embodiments and the first to the fifthcomparison examples, the total of nine phosphors can be manufactured.

FIG. 12 shows excitation spectrums of phosphors respectively inaccordance with the first to the fourth embodiments. FIG. 13 shows lightemission spectrums of phosphors respectively in accordance with thefirst to the fourth embodiments. The light emission spectrum of FIG. 13is obtained when the phosphors according to the first to the fourthembodiments are excited by light having a wavelength of 460 nm. In FIGS.12 and 13, the horizontal axis represents a wavelength (mm) and thevertical axis represents an intensity standardized to 1.

Referring to FIGS. 12 and 13, it can be seen that the phosphorsaccording to the first to the fourth embodiments may be excited byultraviolet ray and light in a blue visible light band close to anultraviolet band and may emit light in a range from a green visiblelight band to a yellow visible light band.

FIG. 14 is a graph showing internal quantum efficiencies based onstrontium ratios of the first to the fourth embodiment and the first tothe fifth comparison examples. The internal quantum efficiency means aratio of emitted light to absorbed light.

The horizontal axis of FIG. 14 represents a ratio of strontium. Thequantum efficiency of the vertical axis is relative based on the thirdembodiment. Referring to FIG. 14, it can be found that the quantumefficiency is high when the ratio of strontium is equal to or greaterthan 0.25 or is equal to or less than 0.55.

FIG. 15 is a graph showing X-ray diffraction patterns of the first tothe fourth embodiment and the first to the fifth comparison examples. InFIG. 15, x-axis represents the incident angle of X-ray and y-axisrepresents the intensity of diffraction. Here, X-ray is anelectromagnetic wave having a wavelength of from 0.05 to 0.25 nm.

Referring to 2θ of the x-axis in FIG. 15, the crystal structures of thephosphors of the first to the fourth embodiments are the triclinicsystem beta (β) and thus, it can be appreciated that it is differentfrom the triclinic system alpha (α), i.e., the crystal structures of thephosphors of the second to the fifth comparison examples.

FIG. 16 shows results obtained by plotting the first to the fourthembodiment and the first to the fifth comparison examples on atriangular diagram representing x, y and z on coordinate axes thereof.It can be seen that the first to the fourth embodiments are includedwithin the range of the phosphor according to the embodiment of thepresent invention.

Additionally, the following Table 3 shows the crystal structures andlattice constants of the first to the fourth embodiments and the firstto the fifth comparison examples.

TABLE 3 first second third fourth fifth comparison first second thirdfourth comparison comparison comparison comparison example embodimentembodiment embodiment embodiment example example example example crystalstructure triclinic triclinic triclinic triclinic triclinic triclinictriclinic triclinic lattice monoclinic system beta system beta systembeta system beta system beta system beta system beta system betaconstant system (β) (β) (β) (β) (α) (α) (α) (α) a(Å) 7.3570 7.71387.7239 7.7654 7.7831 7.0430 7.0490 7.0644 7.0993 b(Å) 13.6442 27.586227.5432 27.8532 28.0758 7.1699 7.1786 7.2006 7.2493 c(Å) 10.4965 7.32917.3612 7.3725 7.3791 7.2251 7.2483 7.2544 7.2780 α(°) 90.0000 90.487390.5420 90.6617 90.7539 88.7002 88.7463 88.7024 88.7942 β(°) 101.8445112.7451 112.8296 112.5600 112.3659 84.7876 88.7658 84.7388 84.8196

 (°) 90.0000 89.6602 89.5397 90.8188 91.0972 75.9613 75.8454 75.766875.8919 V(Å³) 1031.2000 1436.8335 1443.2599 1472.1919 1490.5238 352.4909354.1673 356.1848 361.7778

Referring to FIGS. 14 and 15 and Table 3, it can be understood that whenthe ratio of strontium (Sr) is from 25% to 55%, the crystal structuresof the phosphors according to the first to the fourth embodiments aretriclinic system beta (β).

Through the lattice constant difference, it can be seen that thetriclinic system beta (β) of the phosphors according to the first to thefourth embodiments is different from the triclinic system alpha (α) ofthe phosphors according to the second to the fifth comparison examples.The crystal structure of generally well-known SrSi₂N₂O₂ is triclinicsystem alpha (α). Therefore, it can be noted that the crystal structuresof the phosphors according to the first to the fourth embodiments aredifferent from that of SrSi₂N₂O₂.

Referring to Table 3, a unit cell volume of the triclinic system beta(β) crystal structure of the phosphors according to the first to thefourth embodiments is greater than 700 Å³ In other words, the unit cellvolume of the triclinic system beta (β) is more than twice as much asthe unit cell volume of triclinic system alpha (α).

Also, the phosphors according to the first to the fourth embodimentshave higher light emitting luminance than those of CaSi₂N₂O₂:Eu andSrSi₂N₂O₂:Eu.

<Light Emitting Device>

FIG. 1 is a cross sectional view of a light emitting device according tothe embodiment. FIG. 1 shows a surface mount-type light emitting device.

Referring to FIG. 1, the light emitting device according to theembodiment may include a body 100, a first and a second lead frames 110a and 110 b, a light emitting element 120, a wire 130 and a lighttransmissive resin 140.

The first and the second lead frames 110 a and 110 b are disposed in thebody 100. The body 100 has a recess receiving the light emitting element120, the wire 130 and the light transmissive resin 140.

The first and the second lead frames 110 a and 110 b are apart from eachother on the bottom of the recess of the body 100. The light emittingelement 120 is disposed on the first lead frame 110 a. The first leadframe 110 a is electrically connected to one electrode of the lightemitting element 120 through the wire 130. The second lead frame 110 bis electrically connected to another electrode of the light emittingelement 120 through the wire 130.

The light emitting element 120 is disposed in the recess of the body 100and disposed on the first lead frame 110 a. The light emitting element120 generates light by means of voltage applied to the first and thesecond lead frames 110 a and 110 b.

The light emitting element 120 may be a light emitting diode.Specifically, the light emitting element 120 may be a light emittingdiode which is implemented by one of a horizontal type chip, a flip-chipand a vertical type chip.

When the voltage is applied to the light emitting element 120, the lightemitting element 120 is able to emit light having a peak wavelength in400 to 480 nm band. Here, the light emitting element 120 may be an InGaNlight emitting diode chip which emits ultraviolet ray or light having ablue wavelength close to the ultraviolet ray.

The light emitting element 120 may be not only the light emitting diodebut also a laser diode having a peak wavelength in the same wavelengthband, a side light emitting laser diode, an inorganic electro fieldlight emitting element and an organic electro field light emittingelement.

The wire 130 is disposed in the recess of the body 100 and electricallyconnects the first and the second lead frames 110 a and 110 b to thelight emitting element 120.

The light transmissive resin 140 is disposed in the recess of the body100. The light transmissive resin 140 molds the light emitting element120 and the wire 130. The light transmissive resin 140 transmits thelight emitted from the light emitting element 120. The lighttransmissive resin 140 may be an epoxy resin, a silicone resin, apolyimide resin, a urea resin and an acrylic resin.

As shown in the drawing, the light transmissive resin 140 may moldaround the entire light emitting element 120 or may mold partially apredetermined light emitting portion of the light emitting element 120if necessary. For example, when the light emitting element 120 is a lowpower light emitting element, it is preferable to mold the entire lightemitting element 120. When the light emitting element 120 is a highpower light emitting element, it is preferable to mold partially thelight emitting element 120 for the purpose of the uniform distributionof phosphors 141.

The light transmissive resin 140 includes the phosphor 141 according tothe embodiment. The phosphor 141 is excited by a part of light emittedfrom the light emitting element 120 and emits light having a wavelengthdifferent from that of the light emitted from the light emitting element120. The phosphor 141 may be a single phosphor or may include variousphosphors. For instance, the phosphor 141 may include at least one ofyellow, green and red phosphors. The yellow phosphor emits light havinga dominant wavelength in a wavelength band from 540 nm to 585 nm inresponse to blue light (430 nm to 480 nm). The green phosphor emitslight having a dominant wavelength in a wavelength band from 510 nm to535 nm in response to the blue light (430 nm to 480 nm). The redphosphor emits light having a dominant wavelength in a wavelength bandfrom 600 nm to 650 nm in response to the blue light (430 nm to 480 nm).The yellow phosphor may be a silicate phosphor or a YAG-based phosphor.The green phosphor may be the silicate phosphor, a nitride phosphor or asulfide phosphor. The red phosphor may be the nitride phosphor or thesulfide phosphor.

FIG. 2 is a cross sectional view of a light emitting device according toanother embodiment. The light emitting device shown in FIG. 2 is formedin the form of a vertical lamp type.

The light emitting device shown in FIG. 2 may include a first and thesecond lead frames 210 a and 210 b, a light emitting element 220, a wire230, a light transmissive resin 240 and an external material 250.

The first and the second lead frames 210 a and 210 b are disposed apartfrom each other. The light emitting element 220 is disposed on the firstlead frame 210 a. The first lead frame 210 a is electrically connectedto one electrode of the light emitting element 220 through the wire 230.The second lead frame 210 b is electrically connected to anotherelectrode of the light emitting element 220 through the wire 230.

The light emitting element 220 is disposed on the first lead frame 210a. The light emitting element 220 generates light by means of voltageapplied to the first and the second lead frames 210 a and 210 b.

The light emitting element 220 may be a light emitting diode.Specifically, the light emitting element 220 may be a light emittingdiode which is implemented by one of a horizontal type chip, a flip-chipand a vertical type chip.

When the voltage is applied to the light emitting element 220, the lightemitting element 220 is able to emit light having a peak wavelength in400 to 480 nm band. The light emitting element 220 may be an InGaN lightemitting diode chip which emits ultraviolet ray and light having a bluewavelength close to the ultraviolet ray.

The light emitting element 220 may be not only the light emitting diodebut also a laser diode having a peak wavelength in the same wavelengthband, a side light emitting laser diode, an inorganic electro fieldlight emitting element and an organic electro field light emittingelement.

The wire 230 electrically connects the first and the second lead frames210 a and 210 b to the light emitting element 220.

The light transmissive resin 240 is disposed on the first lead frame 210a and molds the light emitting element 220. The light transmissive resin240 also molds a portion of the wire 230 connected to the light emittingelement 220. The light transmissive resin 240 transmits the lightemitted from the light emitting element 220. The light transmissiveresin 240 may be an epoxy resin, a silicone resin, a polyimide resin, aurea resin and an acrylic resin.

The light transmissive resin 240 may mold around the entire lightemitting element 220 or may mold partially a predetermined lightemitting portion of the light emitting element 220 if necessary.

The light transmissive resin 240 includes a phosphor 241 according tothe embodiment. The phosphor 241 is excited by a part of light emittedfrom the light emitting element 220 and emits light having a wavelengthdifferent from that of the light emitted from the light emitting element220. The phosphor 241 may be a single phosphor or may include variousphosphors. For instance, the phosphor 241 may include at least one ofyellow, green and red phosphors. The yellow phosphor emits light havinga dominant wavelength in a wavelength band from 540 nm to 585 nm inresponse to blue light (430 nm to 480 nm). The green phosphor emitslight having a dominant wavelength in a wavelength band from 510 nm to535 nm in response to the blue light (430 nm to 480 nm). The redphosphor emits light having a dominant wavelength in a wavelength bandfrom 600 nm to 650 nm in response to the blue light (430 nm to 480 nm).The yellow phosphor may be a silicate phosphor or a YAG-based phosphor.The green phosphor may be the silicate phosphor, a nitride phosphor or asulfide phosphor. The red phosphor may be the nitride phosphor or thesulfide phosphor.

The external material 250 molds a portion of the first and the secondlead frames 210 a and 210 b and the entire light emitting element 220,the entire wire 230 and the entire light transmissive resin 240.Therefore, the portions other than the molded portion of the first andthe second lead frames 210 a and 210 b are exposed to the outside of theexternal material 250.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to affect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A phosphor which emits light having a peakwavelength between a green wavelength band and a yellow wavelength band,has a crystal structure of which the chemical formula is MSi₂N₂O₂,M=Ca_(x)Sr_(y)Eu_(z) (x+y+z=1), and has a triclinic system crystalstructure in which, when molar ratios of Ca, Sr and Eu are x, y and zrespectively, x+y+z=1 and when the x, y and z are represented by atriangular projection, the x, y and z are distributed on the lines andat the inside of an area formed by connecting five points of (0.45,0.55, 0), (0.75, 0.25, 0), (0.75, 0, 0.25), (0.5, 0, 0.5) and (0.45,0.05, 0.5) by a solid line on a triangular diagram.
 2. The phosphor ofclaim 1, wherein, when x, i.e., the molar ratio of Ca, y, i.e., themolar ratio of Sr and z, i.e., the molar ratio of Eu are represented ona triangular diagram (x, y, z), the x, y and z are located on the linesand at the inside of an area formed by connecting points of A (0.45,0.55, 0), B (0.75, 0.25, 0), C (0.7, 0, 0.3) and D (0.5, 0, 0.5) asvertices.
 3. The phosphor of claim 1, wherein, when x, i.e., the molarratio of Ca, y, i.e., the molar ratio of Sr and z, i.e., the molar ratioof Eu are represented on a triangular diagram (x, y, z), the x, y and zare located on the lines and at the inside of an area formed byconnecting points of A (0.45, 0.4, 0.15), B (0.75, 0.1, 0.15), C (00.75,0, 0.25), D (0.6, 0, 0.4) and E (0.45, 0.15, 0.4) as vertices.
 4. Thephosphor of claim 1, wherein the molar ratio z of Eu is within a rangefrom 0.15 to 0.4 (0.15≦z≦0.4).
 5. The phosphor of claim 1, wherein themolar ratio y of Sr is within a range from 0.2375 to 0.475(0.2375≦y≦0.475).
 6. The phosphor of claim 1, wherein the molar ratio yof Sr is within a range from 0.25 to 0.55 (0.25≦y≦0.55).
 7. The phosphorof claim 1, wherein the peak wavelength is from 540 nm to 585 nm.
 8. Thephosphor of claim 1, wherein a unit cell volume of the triclinic systemcrystal structure is greater than 700 Å³.
 9. The phosphor of claim 1,wherein the phosphor comprises a beta (β) crystal structure of thetriclinic system.
 10. A phosphor which emits light having a peakwavelength between a green wavelength band and a yellow wavelength band,has a crystal structure of which the chemical formula is MSi₂N₂O₂,M=Ca_(x)Sr_(y)Eu_(z) (x+y+z=1), and has a triclinic system crystalstructure in which, when molar ratios of Ca, Sr and Eu are x, y and zrespectively, x+y+z=1 and when the x, y and z are represented by atriangular projection, the x, y and z are distributed on the lines andat the inside of an area formed by connecting five points of (0.45, 0.4,0.15), (0.75, 0.1, 0.15), (0.75, 0, 0.25), (0.6, 0, 0.4) and (0.45,0.15, 0.4) by a solid line on a triangular diagram, wherein a unit cellvolume of the triclinic system crystal structure is greater than 700 Å³.11. The phosphor of claim 10, wherein the molar ratio z of the Eu iswithin a range from 0.15 to 0.4 (0.15≦z≦0.4).
 12. The phosphor of claim10, wherein the molar ratio y of the Sr is within a range from 0.2375 to0.475 (0.2375≦y≦0.475).
 13. The phosphor of claim 10, wherein the molarratio y of the Sr is within a range from 0.25 to 0.55 (0.25≦y≦0.55). 14.The phosphor of claim 10, wherein the peak wavelength is from 540 nm to585 nm.
 15. The phosphor of claim 10, wherein the phosphor comprises abeta (β) crystal structure of the triclinic system.
 16. A light emittingdevice comprising: a light emitting element; and a phosphor which isexcited by a part of light emitted from the light emitting element andemits light having a wavelength different from that of the light emittedfrom the light emitting element, wherein the phosphor emits light havinga peak wavelength between a green wavelength band and a yellowwavelength band, has a crystal structure of which the chemical formulais MSi₂N₂O₂, M=Ca_(x)Sr_(y)Eu_(z) (x+y+z=1), and has a triclinic systemcrystal structure in which, when molar ratios of Ca, Sr and Eu are x, yand z respectively, x+y+z=1 and when the x, y and z are represented by atriangular projection, the x, y and z are distributed on the lines andat the inside of an area formed by connecting five points of (0.45,0.55, 0), (0.75, 0.25, 0), (0.75, 0, 0.25), (0.5, 0, 0.5) and (0.45,0.05, 0.5) by a solid line on a triangular diagram.
 17. The lightemitting device of claim 16, wherein the molar ratio z of Eu is within arange from 0.15 to 0.4 (0.15≦z≦0.4).
 18. The light emitting device ofclaim 16, wherein the molar ratio y of the Sr is within a range from0.2375 to 0.475 (0.2375≦y≦0.475).
 19. The light emitting device of claim16, wherein the molar ratio y of the Sr is within a range from 0.25 to0.55 (0.25≦y≦0.55).
 20. The light emitting device of claim 16, whereinthe peak wavelength is from 540 nm to 585 nm.